The ability to create, support and manipulate single walled magnetic domains in selected materials under proper operating conditions has led to the utilization of devices having the afore-mentioned ability for performing storage and retrieval functions akin to that encountered in computers and related apparatus. A particular class of devices for performing a memory function employing single walled domains (more popularly termed bubbles, as they will be termed hereinafter) is the so-called bubble lattice file.
Bubble lattice files and apparatus particularly useful therewith are disclosed in Voegeli, U.S. Pat. No. 3,930,244; Hu et al, U.S. Pat. No. 3,953,842; and Rosier, U.S. Pat. No. 3,913,079, all assigned to the assignee of this application, and in an article entitled "Data Organization in Magnetic Bubble Lattice Files" by C. K. Wong and P. C. Yue, appearing in Volume 20, Number 6 of the IBM Journal of Research and Development (November 1976), pages 576-581.
A bubble lattice file (hereinafter BLF) operates very differently from the more familiar bubble devices in which streams of bubbles propagate synchronously with a reorienting magnetic field. More particularly, in BLF's, bit information is encoded in the wall states of magnetic bubble domains, rather than in the absence or presence of bubbles at certain locations. Bit information is decoded by detecting the direction of movement of bubbles at a sensor under a deflecting field gradient.
A BLF thus includes a lattice or matrix of bubbles in which every position in the lattice is filled. This imparts stability to the BLF since the bubbles interact and tend to support their neighbors.
As disclosed in U.S. Pat. No. 3,930,244, a stable BLF supported on a suitable material is provided with one or more devices for accessing the bubbles contained in the lattice as well as propagation means so that the lattice can be translated with respect to the accessing devices. By their nature, each accessing device or channel is capable of accessing, that is, reading out or writing into any one or all bubble domain positions in the lattice aligned with the channel. Thus, for example, if we consider a bubble lattice to be arranged with rows and columns, the access devices may be, for example, aligned with selected columns of the lattice. Under those circumstances, any one or all of the bubble domains in the columns aligned with the accessing devices can be accessed, that is, the bubbles can be read out or rewritten in accordance with externally applied information. Substantially similar results are obtained if the access channels align with rows instead of columns, and rows and columns need not be perpendicular. As further disclosed in the patent, access is enabled with regard to bubbles not in the columns aligned with the accessing devices by translating the lattice, as a whole, to align a column including the desired bubble or bubbles with one of the accessing devices or channels. One arrangement for translating a bubble lattice for accessing purposes is disclosed in an article entitled "Bubble Lattice Translation - Analysis" by John S. Eggenberger, appearing in the Proceedings of the Twentieth Annual Conference on Magnetism and Magnetic Materials (Dec. 3-6, 1974 pages 622-623).
As presently contemplated, a significant function to be performed by a BLF is a sorting function in which an initial form of the lattice will be transformed by rearranging the order in which bubble columns appear. Such a rearrangement can be effected simply by an interative process of exchanging bubble columns by, for example, coupling a pair of access channels. In this regard, the Wong et al article entitled "Data Organization in Magnetic Bubble Lattice Files" appearing in the IBM Journal of Research and Development, Volume 20, Number 6, November 1976, pages 576-581, teaches how adjacent columns can be interchanged. Those of ordinary skill in the art will readily understand, however, that non-adjacent columns can be interchanged by suitably controlling selected switches connecting column accessing devices so long as each is simultaneously adjacent or aligned with an appropriate access channel. It should readily be apparent that multiplying the number of access channels will speed the sorting process by reducing the number of times the BLF has to be translated to align desired columns with an access channel. For example, at one extreme, employing an access channel for each column in the BLF eliminates the necessity for any translation of the BLF. In most applications, however, providing an access channel for each column in the BLF will not be practical.
Thus, for most application, the number of access channels that can be provided will be some number less than the total number of columns in the BLF. Generally, the number of access channels will be vastly smaller than the number of columns in the BLF. The problem to which this invention is directed, then, is how are the access channels to be arranged in the BLF so as to provide for small operating times of the BLF.
It is therefore an object of the invention to provide a method of organizing a bubble lattice file which includes a plurality of access channels, less than the number of columns in the BLF. It is a further object of the invention to provide a BLF in which at least some access channels are arranged so as to facilitate rapid sorting of BLF columns.
Plural access channels are provided, each of which can read or write into an aligned column so that any aligned column can be exchanged with any other aligned column. However, we have found that this capability is unnecessary, at least for sorting operations. Effective and efficient sorting only requires the capacity to interchange an aligned column with the column aligned with the access channel in the reference position.